Controlling power and access of wireless devices to base stations which use code division multiple access

ABSTRACT

The invention relates to the use of CDMA techniques. Data signals to be transmitted from a plurality of wireless devices are spread across a common bandwidth. The data signals are received by a base station as a composite spread signal. The base station partially despreads the composite spread signal with unique codes to extract data signals from individual wireless devices. The data rate and quality of service requirements for each wireless device are used to calculate a power factor and a control signal is sent to control the power from a particular wireless device. In addition, a probability of transmission value is calculated based on an equivalent current load value and an equivalent population value. The probability of transmission value determines whether a particular wireless device is allowed access to an uplink frequency channel.

FIELD OF THE INVENTION

This invention relates to the field of wireless communications. Moreparticularly it relates to more efficient use of a designated frequencyspectrum by code division multiple access (CDMA) techniques and accessprotocols.

BACKGROUND OF THE INVENTION

The recent growth in the use of wireless communication devices, such asmobile telephones, wireless local area networks (LANs) and wirelessprivate branch exchanges (PBXs) has strained the capacity of theelectromagnetic frequency spectrum these devices use. Various techniqueshave been proposed and used for determining which wireless devices aregiven access to the available frequency spectrum and for efficientlyusing the available frequency spectrum.

In order to communicate, a wireless device must typically first gainaccess to an uplink frequency channel of a base station. Base stationstypically give access to one wireless device on a single uplinkfrequency channel based on known protocols such as ALOHA and Busy-Tone.In both of these protocols, a wireless device transmits a request signalto a base station on a request frequency channel and if there are noother wireless devices transmitting request signals at that moment,access to an uplink frequency channel is granted. These protocols whileadequate for servicing voice communications on circuit switched networksare not adequate to service sources which transmit bursts of informationon packet switched networks.

In addition to protocols which determine which single wireless device isallowed access to a single uplink frequency channel, techniques forpermitting the simultaneous access by multiple wireless devices to asingle uplink frequency channel of a base station are known. One ofthese techniques is code division multiple access (CDMA). In CDMA, adigital signal located at a wireless device is multiplied at thewireless device by a unique code corresponding to that device, whichspreads the digital signal over a greater bandwidth. For example, a 10kHz digital signal may be multiplied by a code which effectively createsa 100 kHz spread digital signal.

The spread digital signal is used to modulate a carrier frequency signalwhich is in the range of the uplink frequency channel and the modulatedcarrier is transmitted from the wireless device to the base station. Thebase station receives a composite spread signal of all the modulatedcarrier frequency signals from all wireless devices transmitting at thatpoint in time. The base station demodulates the composite spread signaland then partially despreads the demodulated signal using the sameunique code used at a particular wireless device for spreading. Thepartially despread signal approximates the pre-spreading data signal forthe particular wireless device.

Despreading causes the signal from a particular wireless device to havea power advantage over signals from other wireless devicessimultaneously transmitting and thus allows the signal from thatparticular wireless device to be separated from the signals from theother wireless devices. The power advantage for a particular wirelessdevice is proportional to the spreading bandwidth divided by the datarate for that wireless device. Thus spreading undesirably causeswireless devices with lower data rates to have greater power advantagesand consequently greater quality of service than wireless devices withhigher data rates.

A new approach for CDMA access by a plurality of wireless devices isneeded for wireless devices which have differing data rates anddiffering quality of service requirements.

SUMMARY OF THE INVENTION

The present invention in one embodiment provides a method and apparatusfor determining the type of a particular wireless device and controllingthe power transmitted by a wireless device based on the type of wirelessdevice. Preferably, the type is defined by the data rate and quality ofservice requirements for the wireless device. The power transmitted by aparticular wireless device is controlled so that the ratio of the powerreceived at a base station receiving antenna from the particularwireless device to a minimum power level is proportional to the ratio ofthe data rate of that device to a minimum data rate. In addition, thepower transmitted by the particular wireless device is controlled suchthat the ratio of the power received from the particular wireless deviceto a minimum power level is proportional to the ratio of the quality ofservice requirement of that device to a minimum quality of servicerequirement. The base station of the present invention preferablyemploys CDMA technology through the use of a despreader.

The present invention in another embodiment provides a method andapparatus for determining whether a particular wireless device is givenaccess to an uplink frequency channel based on an equivalent populationvalue and an equivalent current load value. Wireless devices with higherpower levels as required by higher data rates or higher quality ofservice requirements are given proportionately higher current loadshares and population shares for determining an equivalent populationvalue and an equivalent current load value respectively.

The equivalent current load and equivalent population values arepreferably used by a base station to determine probability oftransmission values for wireless devices of particular types. The typeof wireless device is preferably defined by the device's data rate andits quality of service requirement. The probability of transmissionvalue is used by a random generator, preferably at the base station, todetermine when a wireless device is permitted access to an uplinkfrequency channel. Alternatively, the base station may transmitequivalent current load and equivalent population values to wirelessdevices of a particular type and those wireless devices can thendetermine the probability of transmission value.

The present invention permits the statistical multiplexing of a largenumber of different types of wireless devices with different data ratesand quality of service requirements. It also allows peak capacity accessby one wireless device when all other wireless devices are idle.Furthermore, the present invention allows for the setting of prioritiesfor fair capacity sharing among all busy wireless devices and makesefficient use of the available frequency spectrum.

The above discussed features, as well as additional features andadvantages of the present invention will become more readily apparent byreference to the following detailed description and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a base station and two wirelessdevices;

FIG. 2A illustrates a power spectral density function at a basestation's receiver/transmitter antenna due to one wireless devicetransmitting data without spreading;

FIG. 2B illustrates a power spectral density function at a basestation's receiver/transmitter antenna due to another wireless devicetransmitting data without spreading;

FIG. 2C illustrates a composite power spectral density function and apartial power spectral density function at a base station'sreceiver/transmitter antenna due to transmission by two wireless devicesafter spreading;

FIG. 2D illustrates conceptually a composite power spectral densityfunction at a base station after partial despreading using a code forone wireless device;

FIG. 2E illustrates conceptually a composite power spectral densityfunction at a base station after partial despreading using a code foranother wireless device;

FIG. 3 illustrates a composite power spectral density function and apartial power spectral density function at a base station'sreceiver/transmitter antenna due to transmission by two wireless devicesafter spreading and power control in accordance with the presentinvention;

FIG. 4 illustrates a composite power spectral density function and apartial power spectral density function at a base station'sreceiver/transmitter antenna due to transmission by two wireless devicesafter spreading and power control in accordance with the presentinvention where the wireless devices have differing quality of servicerequirements;

FIG. 5 is a schematic of a base station which controls the powertransmitted by wireless devices in accordance with the presentinvention;

FIG. 6 is a flow chart of a method for controlling the power transmittedby wireless devices;

FIG. 7 is a schematic of a base station which controls the powertransmitted by wireless devices and generates probability and/or loadand population data for transmission to wireless devices;

FIG. 8 is a schematic of a wireless device which uses probability valuesor load and population data values to control transmission of data;

FIG. 9 is a flow chart for determining equivalent current load values;

FIG. 10 is a flow chart for determining equivalent population values;and

FIG. 11 is a flow chart for transmitting equivalent current load andequivalent population values or probability of transmission values to awireless device.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a simple illustration of two wireless devices 12 and 14 and abase station 22. The wireless devices 12 and 14 includereceiver/transmitter antennas 16 and 18 respectively. Base station 22includes a receiver/transmitter antenna 20. FIG. 1 will be used inconjunction with FIGS. 2A-2E to describe known techniques fortransmission and reception of power from wireless devices with CDMAspreading and without CDMA spreading. Details of a base station andwireless device in accordance with the present invention will bedescribed later.

The wireless devices 12 and 14 transmit access request signals viareceiver/transmitter antennas 16 and 18, respectively, and the accessrequest signals are received by the receiver/transmitter antenna 20 ofthe base station 22. If both wireless devices 12 and 14 are given accessto an uplink frequency channel of the base station 22 then wirelessdevices 12 and 14 transmit data signals to the base station 22.

FIGS. 2A-2E show power spectral density functions at thereceiver/transmitter antenna 20 of the base station 22 of FIG. 1. Powerspectral density P(ω), is shown graphed on the y-axis and frequency inradians, ω, is shown graphed on the x-axis.

FIG. 2A illustrates the power spectral density function 24 at thereceiver/transmitter antenna 20 of FIG. 1 due to data transmission bythe wireless device 12 when spreading is not used. The power spectraldensity function 24 of FIG. 2A has a power spectral density P(ω)=P_(A)at frequencies in the bandwidth ω_(c) ±(R₁ /2), where ω_(c) is thecarrier frequency and R₁ is the data rate of the wireless device 12. Thepower received from wireless device 12 at receiver/transmitter antenna20 equals P_(A) times the data rate R₁.

Similarly, FIG. 2B illustrates the power spectral density function 26 atthe receiver/transmitter antenna 20 of the base station 22 of FIG. 1 dueto the wireless device 14 when spreading is not used. The power spectraldensity function 26 of FIG. 2B has a power spectral density P(ω)=P_(A)/2 at frequencies in the bandwidth ω_(c) ±(R₂ /2), where ω_(c) is thecarrier frequency and R₂ is the data rate of the wireless device 14 ofFIG. 1. The power received equals P₂ /2 times the data rate R₂. In thisinstance the data rate of wireless device 14, which is R₂, is twice thedata rate of wireless device 12, which is R₁.

FIG. 2C illustrates a composite power spectral density function 28 atthe base station receiver/transmitter 20 due to wireless devices 12 and14 both transmitting data signals at a spreading rate of R₃. FIG. 2Cfurther illustrates a partial power spectral density function 30 at thereceiver/transmitter 20 of base station 22 due to the wireless device 12transmitting a data signal at the spreading rate of R₃, where R₃ =2R₂=4R₁. The composite power spectral density function 28 of FIG. 2Ccomprises the partial power spectral density function 30 due to thewireless device 12, which has power spectral density P(ω)=P_(A) /4 atfrequencies in the bandwidth ω_(c) ±R₃ /2, where ω_(c) is the carrierfrequency and ₃ the spreading bandwidth. The total power received atreceiver/transmitter 20 equals P_(A) /2 times the spreading bandwidthR₃. The composite power spectral density function 28 of FIG. 2C furthercomprises the partial power spectral density function due to thewireless device 14, which has a power spectral density P(ω)=P_(A)/2-(P_(A) /4)=(P_(A) /4) at frequencies in the bandwidth ω_(c) ±(R₃ /2).The power spectral density functions due to each wireless device areadded together to form the composite power spectral density function 28in FIG. 2C. The composite power spectral density function 28 has powerspectral density P(ω)=P_(A) /2 at frequencies in the bandwidth ω_(c)±(R₃ /2).

The spreading operation takes place inside each wireless device andcauses all signals to be spread over the same bandwidth or spreadingrate, R₃. The bandwidth of the signal transmitted from the wirelessdevice 12 is spread to four times its data rate and the bandwidth of thesignal transmitted from the wireless device 14 is spread to two timesits data rate. Typically, when CDMA spreading is used, the majority ofwireless devices will have their data signals spread over a much largerbandwidth. The spreading factor F of the base station is the spreadingbandwidth divided by a minimum reference data rate. In this case, F=R₃/R₁ =4.

After spreading, each signal is transmitted from its respective wirelessdevice. The composite spread signal ("CS"), the power spectral densityfunction 28 of which is shown in FIG. 2C, is received by the basestation 22 in FIG. 1 via its receiver/transmitter antenna 20. At thebase station 22, composite spread signals are partially despread by theuse of unique codes which identify particular wireless devices. Eachunique code corresponds to the code used at the particular wirelessdevice for spreading. The unique code transforms the signal transmittedfrom a particular wireless device to prespreading form. However, signalsfrom all other wireless devices remain in their spread form. The effectof despreading of a signal from the wireless device 12 while the signalfrom the wireless device 14 remains spread is shown in FIG. 2D.

FIG. 2D conceptually illustrates a composite power spectral densityfunction 32 after partial despreading of the signal received byreceiver/transmitter 20 of base station 22 by the unique code forwireless device 12. Composite power spectral density function 32 issimilar in shape to power spectral density function 24 for wirelessdevice 12 of FIG. 2A. The partial despreading causes the data signalfrom the wireless device 12 to have a power advantage over the datasignal from the wireless device 14 and noise. This allows the datasignal from wireless device 12 to be extracted. The power advantage isproportional to the spreading bandwidth, R₃, divided by the data ratefor the wireless unit 12, R₁, which is R₃ /R₁ =4.

FIG. 2E conceptually illustrates a composite power spectral densityfunction 34 after partial despreading of the signal received byreceiver/transmitter 20 of base station 22 by the unique code forwireless device 14. Composite power spectral density function 34 issimilar to power spectral density function 26 in FIG. 2B for wirelessdevice 14. The wireless device 14 has a power advantage proportional toR₃ /R₂ =2.

As can be seen from FIGS. 2D and 2E, wireless devices with lower datarates have greater power advantages than wireless devices with higherdata rates. This greater power advantage results in greater quality ofservice for wireless devices with lower data rates. One aspect of thepresent invention controls the power received from wireless devices sothat power advantages are equalized for devices having different datarates but the same quality of service requirements.

In the present invention, the power transmitted by wireless devices withhigher data rates is controlled so that the power received at the basestation from a particular wireless device divided by a reference poweris proportional to the data rate of that particular wireless devicedivided by a minimum reference data rate. The following formula ispreferably satisfied: P/P_(min) =R/R_(min), where P is the powerreceived due to the particular wireless device, P_(min) is a referenceminimum power level, R is the data rate of the particular wirelessdevice, and R_(min) is a minimum reference data rate.

FIGS. 1, 3, and 4 will be used to explain power control in accordancewith the present invention. In FIG. 3, the composite power spectraldensity function 36 at the receiver/transmitter 20 of the base station22 due to transmission by the wireless devices 12 and 14 of FIG. 1 afterpower control is shown. The partial power spectral density function 38due to the wireless device 12 after power control is also shown. Thepower transmitted by wireless device 14 has been controlled such thatthe power received at the receiver/transmitter antenna 20 of the basestation 22 due to wireless device 14 is twice that of the referenceminimum power level, which in this case is the power received from thewireless device 12. The power received from the wireless device 14 isequal to 3P_(A) /4-P_(A) /4=P_(A) /2 times the bandwidth R₃ and thepower received from wireless device 12 is P_(A) /4 times the bandwidth₃. In this manner the power advantage obtained after despreading can beequalized for the wireless devices 12 and 14. The following formula ispreferably satisfied: P₂ /P₁ =R₂ /R₁ =2, where P₁ and P₂ are the powerlevels received at the receiver/transmitter antenna 20 of the basestation 22 from the wireless devices 12 and 14, respectively. R₂ is thedata rate of the wireless device 14 and R₁ is the data rate of thewireless device 12.

The doubling of the power received from the wireless device 14 of FIG. 1permits the same quality of service requirement to be satisfied for bothwireless devices 12 and 14. In this case, satisfying the same quality ofservice requirement is preferably defined as satisfying the same signalto interference ratio.

A similar power control technique is preferable for wireless deviceshaving the same data rate but different quality of service requirements.Assuming the wireless devices have the same data rates, the ratio of thepower received from a particular wireless device divided by a referenceminimum power level is preferably equal to the ratio of the quality ofservice required by the particular wireless device divided by theminimum quality of service required. In other words, the followingformula is preferably satisfied: P/P_(min) =QOS/QOS_(min), where P isthe power received from a particular wireless device; P_(min) is thereference minimum power level; QOS is the quality of service requirementfor the particular wireless device; and QOS_(min) is the minimum qualityof service reference level.

The power control technique of the present invention permits wirelessdevices with the same data rates and different quality of servicerequirements to be controlled to achieve their respective quality ofservice requirements. While FIG. 3 was described for differing datarates and the same quality of service requirements, the results areanalogous for differing quality of service requirements and the samedata rates. For example, if the data rate of the wireless devices 12 and14 is the same but the quality of service required by the wirelessdevice 14 is twice that of the wireless device 12, the desired powerlevels shown in FIG. 3 would be the same. The power transmitted bywireless device 14 would be controlled such that the power received fromthe wireless device 14 is twice the reference minimum power level.

FIG. 4 illustrates the power received at receiver/transmitter antenna 20of the base station 22 of FIG. 1 when both quality of service and datarate requirements differ. In this case, it is assumed that the wirelessdevice 14, which has a data rate twice that of the wireless device 12,also has a quality of service requirement twice that of the wirelessdevice 12. In other words, device 14 requires a 3 dB higher signal tointerference ratio than device 12 for comparable quality of service.Accordingly, the power received at the receiver/transmitter antenna 20from the wireless device 14 should be four times the power received fromthe wireless device 12. Thus, the power transmitted by wireless device14 is controlled such that the power received from the wireless device14 is 5/4*P_(A) -P_(A) /4=P_(A) times the bandwidth R₃ and the powertransmitted from wireless device 12 is controlled such that the powerreceived from wireless device 12 is P_(A) /4 times the bandwidth R₃. Ingeneral, the following formula should be satisfied for wireless deviceswith different data rates and different quality of service requirements:P/P_(min) =R/R_(min) *QOS/QOS_(min), P is the power received due to aparticular wireless device. R and QOS are the data rate and quality ofservice requirements, respectively, of a particular wireless device.P_(min), R_(min), and QOS_(min) are the minimum power level, minimumdata rate and minimum quality of service requirement, respectively.

FIG. 5 illustrates a base station 110 in accordance with the presentinvention and a plurality of wireless devices 172, 174, 176, 178, and180. The base station 110 comprises a receiving antenna 114, a bandpassfilter 122, a memory 128, a despreader 136, a processor 144, atransmitting antenna 152, an admission control antenna 158, an admissionbandpass filter 166, and a memory 196.

The receiving antenna 114 is connected via its output 116 and conductor118 to an input 120 of the bandpass filter 122. The bandpass filter 122is connected via its output 124 and conductor 126 to input/output 134 ofthe despreader 136. The memory 128 is connected via its input/output 130and conductor 132 to an input/output 134 of the despreader 136, which isconnected via an output 138 and a conductor 140 to an input 142 of theprocessor 144. The processor 144 is connected via its output 146 and theconductor 148 to an input 150 of the transmitting antenna 152. Theadmission control antenna 158 is connected via its input/output 160 andthe conductor 162 to input/output 164 of the admission bandpass filter166 which is connected via its input/output 168 and a conductor 170 toan input 142 of the processor 144. The memory 196 is connected via itsinput/output 194 and a conductor 192 to an input/output 190 of theprocessor 144.

The base station of FIG. 5 controls the power of a wireless device suchas one of the wireless devices 172, 174, 176, 178 or 180 in thefollowing manner in accordance with the present invention. A compositespread signal ("CS") corresponding to all transmitting wireless devicesis received at the receiving antenna 114 and sent via the output 116 andthe conductor 118 to the input 120 of the bandpass filter 122. Thefilter 122 is set to the bandwidth of the uplink frequency channel. Afiltered composite spread signal ("FCS") is produced at the output 124and sent via the conductor 126 to the input/output 134 of the despreader136. The despreader 136 preferably demodulates the FCS signal and storesthe demodulated composite spread signal ("DCS") in the memory 128 viathe input/output 134, the conductor 132 and the input/output 130.

After storing the DCS signal the despreader 136 retrieves a code C_(n)for a particular wireless device from the memory 128, via itsinput/output 130, the conductor 132 and the input/output 134 of thedespreader 136. For example, the code C_(n) may identify the wirelessdevice 172. The despreader 136 uses the code C_(n) to partially despreadthe DCS signal to form a partially despread signal ("PDS"). The PDSsignal is used to determine if the particular wireless device 172 istransmitting. If the PDS signal is less than a threshold, wirelessdevice 172 is not transmitting and the despreader 136 retrieves the nextcode, C_(n+1), which for example may be the code identifying thewireless device 174. Despreading techniques are known in the art. See,for example, Pickholtz, Schilling and Milstein, "Theory ofSpread-Spectrum Communications--A Tutorial," IEEE Trans. Communications,Vol. Com-30, No. 5, pp. 855-884, May 1982.

If the PDS signal is greater than a threshold, the PDS signal is assumedto approximate a pre-spread data signal from the wireless device 172.The PDS signal is then sent to the processor 144 via the despreader'soutput 138, the conductor 140, and the processor's input 142. Theprocessor 144 preferably stores the data rate of the PDS signal in thememory 196 via the input/output 190, the conductor 192 and theinput/output 194.

The code C_(n) used to produce the PDS signal is preferably also sent tothe processor 144 by the despreader 136 to identify wireless device 172.The processor 144 receives the PDS signal and the unique code C_(n),corresponding to the wireless device 172, at the input 142 anddetermines the quality of service requirement for this wireless devicebased on the code C_(n). The quality of service requirement for eachwireless device or for a type of wireless device is preferably stored inthe memory 196. The quality of service requirement can be retrieved bythe processor 144 via the input/output 190 the conductor 192 and theinput/output 194 of the memory 196.

The processor 144 uses the data rate which can be determined from thePDS signal and the quality of service requirement which is stored in thememory 196 to determine a power factor PF by which the power receivedfrom the wireless device 172 should exceed the reference minimum powerlevel P_(min). Alternatively, the data rate can be determined from thecode C_(n). The reference minimum power level P_(min) is the powerdesired to be received from a hypothetical or actual wireless devicewhich has the lowest data rate and the lowest quality of servicerequirement. The power factor is preferably determined by the followingformula: PF=QOS/QOS_(min) *R/R_(min), where QOS and R are the quality ofservice and data rate requirements for wireless device 172, andQOS_(min) and R_(min) are the minimum quality of service and data raterequirements.

After the power factor PF is determined, a power control signal is sentfrom the processor 144 via the output 146 and the conductor 148, to theinput 150 of the transmitting antenna 152 of FIG. 5. The power controlsignal preferably includes the unique code C_(n) for identifying thewireless device 172. The transmitting antenna 152 transmits the controlsignal to wireless devices generally. The wireless device 172 extractsthe code C_(n), determines that the code C_(n) is its identificationcode and adjusts or controls the power it transmits based on the controlsignal.

The power control signal from the base station 110 can continually ask awireless device, such as wireless device 172, to increase its poweruntil the power factor at the receiving antenna 114 of the base station110 is satisfied. The power control operation can also be a tuningprocess in which incremental increases or decreases in power arerequested until the power received at the receiving antenna 114 iswithin a specified limit. Other known techniques for requestingincreases in power and ensuring compliance with power requirements canbe used.

The admission control antenna 158 and the admission control bandpassfilter 166 are used to receive admission requests from the wirelessdevices on a separate admission frequency channel. Alternatively,frequency changing means can be employed with the bandpass filter 122 sothat admission requests and data transmissions can occur with the sametransmitting/receiving antenna. In fact, in many systems, admissioncontrol is accomplished with the same antenna as data transmission.Admission control techniques are known in the art. Admission by the basestation 110 of a wireless device effectively registers that wirelessdevice as a member of the base station's population. Admission does notpermit the wireless device to transmit data but rather makes thewireless device eligible to request the ability to transmit data, whichis also called requesting access, at some future time. The admission ofa particular wireless device can be registered in the memory 196.

FIG. 6 is a flow chart 200 illustrating a method according to thepresent invention for controlling power from wireless devices which havedifferent data rates and/or quality of service requirements.

A composite spread signal is received by a receiving antenna, such asthe receiving antenna 114 of FIG. 5, at step 210. The composite spreadsignal ("CS") contains spread signals transmitted by a plurality ofwireless devices, such as the wireless devices 172, 174, 176, 178, and180 of FIG. 5, and is stored preferably in demodulated form in a memory,such as the memory 128 of FIG. 5, at step 212. A despreading code("C_(n) "), which identifies a particular wireless device, for examplethe wireless device 172, and which is stored in a memory, such as thememory 128, is retrieved from the memory 128 in step 214 by adespreader, such as the despreader 136 of FIG. 5. The despreading codeis used to partially despread the CS signal to form a partially despread("PDS") signal. The base station may alternatively have multipledespreaders and/or processors that can process multiple codes inparallel.

The despreader 136 at step 216 determines if the wireless device 172 iscurrently transmitting data or is "active". If the wireless device isnot active, the method loops back and retrieves the unique code(C_(n+1)) for the next wireless device, for example, wireless device174, from the memory at step 214. If the wireless device 172 is active,the PDS signal will be sent along with the identifying code C_(n), to aprocessor, such as processor 144 in FIG. 5, at step 218. The code andthe PDS signal indicate the data rate and the quality of servicerequired for the wireless device 172. Alternatively the code alone maybe used to identify data rate and quality of service requirements. Aprocessor, such as the processor 144 in FIG. 5, receives the code andthe PDS signal and determines the data rate and quality of servicerequirements at step 220. The data rate and the quality of servicerequirements are used to determine a power factor at step 222. The powerfactor preferably satisfies the formula: PF=QOS/QOS_(min) *R/R_(min).

The processor then compares the received power from the wireless device172 with the power required. If an increase or decrease in power isrequired, an appropriate control signal is sent in step 224. The controlsignal may request an incremental power increase or decrease so thatthrough multiple iterations the received power from the wireless devicecomes within the limits required by the wireless device's power factorPF. Alternatively, the control signal may request a single powerincrease or decrease to satisfy the power factor requirement.

At step 226 the despreader determines if there are any despreading codes(C_(n+1), . . . ) left to examine. For example, if only the code for thewireless device 172 in FIG. 5 has been examined, the unique codes forthe wireless devices 174, 176, 178, and 180 would still need to becycled through. If there are further codes to examine, the method 200loops back to step 214 to retrieve the next code. If there are nospreading codes left to examine the method restarts at the firstdespreading code and goes back to step 210 to receive a new compositespread signal.

FIG. 7 is a schematic of another embodiment of a base station 310 inaccordance with the present invention. The base station 310 comprises areceiving antenna 314, a bandpass filter 322, a memory 328, a despreader336, a processor 344, a transmitting antenna 352, an admission controlantenna 358, an admission bandpass filter 366, and a memory 396. Thesecomponents are analogous to similar components in base station 110 inFIG. 5. The base station 310 additionally comprises a processor 376, amemory 377, and a processor 384.

The receiving antenna 314 is connected via its output 316 and theconductor 318 to the input 320 of the bandpass filter 322. The bandpassfilter 322 is connected via its output 324 and the conductor 326 to theinput/output 334 of the despreader 336. The memory 328 is connected viaits input/output 330 and a conductor 332 to the input/output 334 of thedespreader 336, which is connected via its output 338 and the conductor340 to the input 342 of the processor 344. The processor 344 isconnected via its output 346 and the conductor 348 to the input 350 ofthe transmitting antenna 352. The admission control antenna 358 isconnected via its output 360 and the conductor 362 to the input 364 ofthe admission bandpass filter 366, which is connected via its output 368and the conductor 370 to the input 342 of the processor 344. Theprocessor 344 is connected via its output 346 and the conductor 374 toan input 372 of the processor 376. The processor 376 is connected viaits output 378 and the conductor 380 to the input 382 of the processor384, which is connected via its output 386 and the conductors 388 and348 to the input 350 of the transmitting antenna 352. The processor 344is connected via the input/output 390 and the conductor 392 to theinput/output 394 of the memory 396. The processor 376 is connected viathe input/output 371 to the conductor 373 and the input/output 375 tothe memory 377.

The power control operation of the base station 310 is similar to thepower control operation of the base station 110 which has previouslybeen described with reference to FIG. 5. The operation of the processors376 and 384 of the base station 310 will now be described.

The processor 376 receives the data rate and quality of servicerequirement data from the processor 344 via the output 346, conductor374, and the input 372. The processor 376 preferably stores current loadvalues (k_(i), k_(i+1). . . ) in the memory 377 and the current loadvalues for this particular type of wireless device k_(i) is updated viathe output 371, the conductor 373 and the input 375 of the memory 377,if necessary. The current load, k_(i), is the number of active wirelessdevices of a type i where the type is determined by the data rate andthe quality of service requirement.

The total wireless device population of a type i, n_(i), admitted atthis base station, is updated upon admission of a new wireless device oftype i. Admission occurs at some time prior to access and n_(i) isupdated after admission in memory 377 by processor 376. Admission mayoccur on a separate frequency channel such as that determined by theadmission filter 366 in FIG. 7, or on the same frequency channel using areserved despreading code or codes, by techniques known in the art. Anadmission request or registration signal is received at the admissionantenna 358. The signal is subsequently sent through the admissionbandpass filter 366 via the admission antenna output 360, the conductor362 and the input 364. Finally, an admission request is received at theprocessor 344 via the output 368, the conductor 370, and the input 342.

The parameters k_(i), K_(i+1), . . . and n_(i), n_(i+1) . . . are usedto calculate an equivalent current load value K and an equivalentpopulation value N according to the following formulas. ##EQU1##

In the above equations, each ##EQU2## value is a population share N_(i)for devices or type i. Each ##EQU3## value is a current load share K_(i)value for devices of type i. The sum of the populations shares (N_(i),N_(i+1). . . ) equals the equivalent population N_(i). The sum of thecurrent load shares (K_(i), K_(i+1). . . ) equals the equivalent currentload. The equivalent current load value, K, and equivalent populationvalue, N, calculations are based on the principal that wireless deviceswith higher data rates and/or higher quality of service requirementseffectively act as a proportionately higher number of wireless devicesby taking up a larger amount of the available power.

The processor 376 sends the parameters K and N via the output 378 andthe conductor 380 to the input 382 of the processor 384. The processor384 then determines the probability of transmission values for thewireless devices, such as the wireless device 172 of FIG. 5, from theprinciple that the expected value of the equivalent current load at atime t+T, K_(exp), should be less than F. The expected value of theequivalent current load at a time t+T is preferably estimated based onthe equivalent current load K at time t and a doubly stochastic Poissonprobability function.

For a base station servicing wireless devices with the same data rateand the same quality of service requirement the following equation isused:

    K.sub.exp ≦F

    or

    (N-K) (1-e.sup.-T/τ0) P.sub.t =K.sup.-T/τ1 P.sub.tt ≦F.

The expression on the left of the "≦" sign represents K_(exp) at timet+T. The expression (N-K) (1-e^(-T/)τ0) P_(t) represents the equivalentnumber of wireless devices which were not active but which will becomeactive after time delay T. T is the roundtrip time delay fromtransmission of a data signal from an active wireless device toreporting that transmission to another wireless device. The expressionK^(-T/)τ1 P_(tt) represents the equivalent number of wireless deviceswhich were transmitting and will continue to transmit after time delayT. P_(t) is the probability of a new transmission and P_(tt) is theprobability of continuing an ongoing transmission. The expression (N-K)represents the equivalent number of wireless devices which are notcurrently transmitting. K represents the equivalent number of wirelessdevices which are transmitting at time t. The expression (1-e^(-T/)τ0)represents the stochastic probability function that an inactive userwill become active after time delay T. The expression e^(-T/)τ1represents the stochastic probability function that an active user willstay active after the time delay T. F is again the spreading ratio ofthe bandwidth of the uplink frequency channel divided by the minimumdata rate.

If it is assumed that P_(t) is equal to P_(tt) then P_(t) and P_(tt) canbe solved for in the previous equation. P_(t) can also be assumed to bea fraction of P_(tt) so that a priority is given to ongoingtransmissions. In either case, P_(t) and subsequently P_(tt) can besolved for known N, K, the time constants τ₀ and τ₁, and the time delayT.

The previous equation uses a doubly stochastic model for a wirelessdevice which is transmitting as a bursty packetized source. The sourceis either in an ON state where packets are being transmitted to a basestation or an OFF state when they are not. The probability of staying inthe ON state after a particular time delay T is e^(-T/)τ1 and theprobability of changing from the ON state to the OFF state in time delayT is 1-e^(-T/)τ1. The probability of staying in the OFF state after timedelay T is e^(-T/)τ0 and the probability of changing from the ON stateto the OFF state is 1-e^(-T/)τ0. Other modelling functions can be usedto model the activity/inactivity of a wireless device. The ratio of theaverage ON time of a wireless device to the sum of the average ON timeand the average OFF time is generally known as the activity factor,β_(i). For this model, β_(i) =τ₁ /(T₁ +T₀).

For a system comprising wireless devices with two different data ratesor QOS requirements, the following expression can be derived, againusing a doubly stochastic Poisson probability function: ##EQU4##

The expression on the left side of the "≦" sign represents K_(exp) attime t+T. N₁ and N₂ represent population shares for wireless deviceswith a first and second data rate, respectively. K₁ and K₂ representcurrent load shares for wireless devices with a first and second datarate, respectively. P_(t1) and P_(tt1), represent probabilities of newtransmission and ongoing transmission, respectively, for devices withthe first data rate. P_(t2) and P_(tt2) represent probabilities oftransmission for devices with the second rate.

The equation above can be simplified by making the followingassumptions:

    τ.sub.1 =max{τ.sub.11, τ.sub.21 }

    τ.sub.0 =min{τ.sub.10, τ.sub.20 }

For a system with more than two types of wireless devices, theappropriate equation can be simplified by the following assumptions:##EQU5##

With these assumptions it is possible to send only the parameters K andN to wireless devices and allow those wireless devices to calculatetheir own probability of transmission value. Otherwise, all current loadshares (K_(i), K_(i+1). . . ) and population shares (N_(i), N_(i+1). . .) should be transmitted to the wireless devices if the probability oftransmission value calculation is to be determined distributively at thewireless devices.

Wireless devices with particular data rates or quality of servicerequirements can be given priority over other types of wireless devicesby setting one probability value equal to a factor times anotherprobability value as was described for ongoing transmissions versus newtransmissions.

The probability of transmission value is sent to a wireless device fromthe processor 384 in FIG. 7 via its output 386 and the conductors 388and 348, to the input 350 of the transmitting antenna 352. The processor384 preferably produces a probability signal in the form of a digitallymodulated downlink carrier frequency signal for broadcasting to all thewireless devices of a particular type. The probability signal istransmitted from the antenna 352. Alternatively, the processor 376 cansend the load data, in this instance comprising the equivalent currentload value K and equivalent population value N, directly to the wirelessdevice which can determine the probability of transmission value basedon the load data.

FIG. 8 is a schematic of a wireless device 410 in accordance with thepresent invention. The wireless device 410 comprises a receiving antenna414, a bandpass filter 422, a demodulator 462, a processor 430, a randomgenerator 440, a packet generator 448 and a transmitting antenna 456.

The receiving antenna 414 is connected via its output 416 and theconductor 418 to the input 420 of the bandpass filter 422. The bandpassfilter 422 is connected via its output 424, and the conductor 426 to theinput 460 of the demodulator 462. The demodulator 462 is connected viaits output 464 to the conductor 466 and an input 428 of the processor430. The processor 430 is connected via its output 432 and the conductor434 to an input 438 of the random generator 440. The demodulator 462 isconnected via its output 464 and the bypass conductor 436 to an input438 of the random generator 440 which is connected via its output 442and the conductor 444 to an input 446 of the packet generator 448. Thepacket generator 448 is connected via its output 450 and the conductor452 to the input 454 of the transmitting antenna 456.

In operation, a load data modulated signal and/or probability datamodulated signal is received at the wireless device 410 from a basestation, such as the base station 310 of FIG. 7, by receiving antenna414. The modulated signal passes through the bandpass filter 422 via itsinput 420 and its output 424. The filtered signal is demodulated by thedemodulator 462 and is sent via the output 464 and the conductor 466 tothe input 428 of the processor 430. The processor 430 calculates aprobability of transmission value for this wireless device based on theload data received. The load data will normally include an equivalentcurrent load value K and an equivalent population value N, which havebeen described with reference to the base station of FIG. 7.

After the probability of transmission value for the wireless device 410is determined by the processor 430, it is sent from the processor 430via its output 432 and conductor 434 to the input 438 of the randomgenerator 440. The random generator 440 produces a random number basedon the given probability value and the random number determines iftransmission from the wireless device 410 will occur at this particulartime. If transmission should occur, the random generator 440 produces anenable signal at its output 442 and sends the enable signal to thepacket generator 448 via conductor 444 and input 446. The packetgenerator 448 will then be enabled to send packets via its output 450and the conductor 452 to input 454 of the transmitting antenna 456 fortransmission. Alternatively, operations performed by processor 430,random generator 440, and packet generator 448 can be combined into asingle processor.

Further, the signal from the demodulator 462 may be sent from its output464 through the bypass conductor 436 directly to the input 438 of therandom generator 440. This can occur if the base station is transmittingprobability of transmission values instead of load data. Other thanbypassing the processor 430, the remaining operation of the circuit ofFIG. 8 would be as described previously.

Referring to FIGS. 9, 10, and 11, a method for statistically controllingtransmission by wireless devices through a base station, such as thebase station 310 of FIG. 7, is shown.

FIG. 9 is a flow chart 500 of the update operation of the equivalentcurrent load value, K, which occurs when a wireless device transmits amodulated spread signal to the base station. The modulated spread signalis received at step 502 and is partially despread by a despreader, suchas the despreader 336 in FIG. 7, using a unique code at step 504. Thepartially despread signal ("PDS") is then demodulated at step 506 andthe data rate and quality of service requirements are determined fromthe demodulated signal and the code used for partial despreading. Thevalue for the number of active wireless devices of type i, k_(i) isstored in a memory, such as the memory 377 in FIG. 7, and is incrementedif this is a new active wireless device, in step 508. The equivalentcurrent load value K, also stored in memory, is then updated at step 510based on the new value k_(i) and the values (k_(i+1), k_(i+2), . . . )and the data rate and quality of service requirements for all activewireless devices as previously described. Alternatively the equivalentcurrent load value K can be updated independently of updates to aparticular k_(i) by sampling all k_(i) 's after particular intervals oftime. In addition, current load shares K_(i) can be calculated aspreviously described.

FIG. 10 is a flow chart 600 for the update operation of the equivalentpopulation value N by a processor such as the processor 376 in FIG. 7.An admission request which includes the type of wireless device isreceived at step 602 via an admission receiver, such as the receiver 358in FIG. 7. If the new wireless device is admitted, the population ofthat type of wireless device, n_(i), is updated and stored in a memorysuch as the memory 377 at step 604. The new n_(i), is then used toupdate the equivalent population value, N, which is also stored in thememory at step 606. Alternatively, the equivalent population value N canbe updated independently of updates to a particular n_(i) by a processorsampling all n_(i) 's in memory (n_(i), n_(i+1), . . . ) afterparticular intervals of time. Population shares N_(i), can also becalculated as previously described.

FIG. 11 is a flow chart 700 for the transmission of load data orprobability data in accordance with the present invention. Values forthe equivalent population value N and the equivalent current load valueK, are retrieved at step 702 by a processor such as the processor 376from a memory, such as the memory 377 of FIG. 7. N and K can betransmitted to wireless devices at step 704 so that the wireless devicescan determine the probability of transmission values. Optionally, theprobability of transmission values can be determined by the base stationat step 706 from N and K. The probabilities can then be transmitted towireless devices at step 708.

The present invention provides the capability of adequately servicingwireless devices with different data and different quality of servicerequirements. The statistical access technique of the present inventionprovides for efficient use of a designated frequency spectrum whereinaccess to a base station can be prioritized for different types ofwireless devices.

We claim:
 1. A base station for controlling the power transmitted by aplurality of wireless devices of mixed types comprising:a transmittingantenna; a receiving antenna; and a processor for receiving a signalfrom the receiving antenna, for recognizing the type of a particularwireless device which is transmitting the signal, wherein the type ofthe particular wireless device is at least partially defined by the datarate of the particular wireless device, and for producing a controlsignal which is sent to and transmitted by the transmitting antenna, thecontrol signal containing control data based on the recognized type ofthe particular wireless device which may be utilized by the particularwireless device to control the power transmitted to the base station bythe particular wireless device.
 2. The base station of claim 1 whereinthe type of the particular wireless device is at least partially definedby the quality of service requirement of the particular wireless device.3. The base station of claim 2 wherein the control signal controls thepower transmitted by the particular wireless device such that wirelessdevices with proportionately higher quality of service requirementsproduce proportionately higher power levels and wireless devices withproportionately higher data rates produce proportionately higher powerlevels at the base station receiving antenna.
 4. The base station ofclaim 1 wherein the control signal controls the power transmitted by theparticular wireless device such that wireless devices withproportionately higher data rates produce proportionately higher powerlevels at the base station receiving antenna.
 5. A base station forcontrolling the power transmitted by a plurality of wireless devices ofmixed types comprising:a transmitting antenna; a receiving antenna; anda processor for receiving a signal from the receiving antenna, forrecognizing the type of a particular wireless device which istransmitting the signal, wherein the type of the particular wirelessdevice is at least partially defined by the quality of servicerequirement of the particular wireless device, and for producing acontrol signal which is sent to and transmitted by the transmittingantenna, the control signal containing control data based on therecognized type of the particular wireless device which may be utilizedby the particular wireless device to control the power transmitted tothe base station by the particular wireless device.
 6. The base stationof claim 5 wherein the control signal controls the power transmitted bythe particular wireless device such that wireless devices withproportionately higher quality of service requirements produceproportionately higher power levels at the base station receivingantenna.
 7. A method for controlling the power transmitted by wirelessdevices of mixed types comprising:receiving at a base station a datasignal from a particular wireless device; determining at the basestation the type of the particular wireless device, wherein the type ofthe particular wireless device is at least partially defined by the datarate of the particular wireless device; and sending a control signalfrom the base station to control the power transmitted by the particularwireless device based on the determination of the type of the particularwireless device.
 8. The method of claim 7 wherein the control signalcontrols the power transmitted by the particular wireless device suchthat wireless devices with proportionately higher data rates produceproportionately higher power levels as received at the base stationantenna.
 9. A method for controlling the power transmitted by wirelessdevices of mixed types comprising:receiving at a base station a datasignal from a particular wireless device; determining at the basestation the type of the particular wireless device, wherein the type ofthe particular wireless device is at least partially defined by thequality of service requirement of the particular wireless device; andsending a control signal from the base station to control the powertransmitted by the particular wireless device based on the determinationof the type of the particular wireless device.
 10. The method of claim9, wherein the type of the particular wireless device is at leastpartially defined by the data rate of the particular wireless device.11. The method of claim 10 wherein the control signal controls the powertransmitted by the particular wireless device such that wireless deviceswith proportionately higher quality of service requirements produceproportionately higher power levels as received at the base stationantenna and wireless devices with proportionately higher data ratesproduce proportionately higher power levels as received at the basestation antenna.
 12. The method of claim 9 wherein the control signalcontrols the power transmitted by the particular wireless device suchthat wireless devices with proportionately higher quality of servicerequirements produce proportionately higher power levels as received atthe base station antenna.
 13. A base station for controlling the powertransmitted by wireless devices of mixed types comprising:a transmittingantenna; a receiving antenna for receiving a composite spread signal; amemory for storing a unique code for each wireless device; a despreaderwhich retrieves the unique code which corresponds to a particularwireless device which is transmitting from the memory and uses theunique code to partially despread the composite spread signal to form apartially despread signal; and a processor for determining the type ofthe particular wireless device, wherein the type of the particularwireless device is defined at least in part by the data rate of theparticular wireless device, and for determining the power received atthe base station receiving antenna from the particular wireless device,and for producing a control signal based on the type of the particularwireless device for controlling the power transmitted by the particularwireless device, wherein the control signal is sent to the transmittingantenna and transmitted.
 14. The base station of claim 13 wherein thecontrol signal controls the power transmitted by the particular wirelessdevice such that wireless devices with proportionately higher data ratesproduce proportionately higher power levels at the receiving antenna ofthe base station.
 15. A base station for controlling the powertransmitted by wireless devices of mixed types comprising:a transmittingantenna; a receiving antenna for receiving a composite spread signal; amemory for storing a unique code for each wireless device; a despreaderwhich retrieves the unique code which corresponds to a particularwireless device which is transmitting from the memory and uses theunique code to partially despread the composite spread signal to form apartially despread signal; and a processor for determining the type ofthe particular wireless device, wherein the type of the particularwireless device is defined at least in part by the quality of servicerequirement for the particular wireless device, and for determining thepower received at the base station receiving antenna from the particularwireless device, and for producing a control signal based on the type ofthe particular wireless device for controlling the power transmitted bythe particular wireless device, wherein the control signal is sent tothe transmitting antenna and transmitted.
 16. The base station of claim15 wherein the type of the particular wireless device is defined atleast in part by the data rate of the particular wireless device. 17.The base station of claim 15 wherein the control signal controls thepower transmitted by the particular wireless device such that wirelessdevices with proportionately higher quality of service requirementsproduce proportionately higher power levels at the receiving antenna ofthe base station antenna of the base station.
 18. The base station ofclaim 17 wherein the control signal controls the power transmitted bythe particular wireless device such that wireless devices withproportionately higher data rates produce proportionately higher powerlevels at the receiving antenna of the base station.
 19. A method forcontrolling the power transmitted by wireless devices of mixed typescomprising:receiving a composite spread signal of the signalstransmitted by a plurality of wireless devices; retrieving a unique codefrom memory corresponding to a particular wireless device which istransmitting and using the unique code to partially despread thecomposite spread signal; determining the current power received from andthe type of the particular wireless device, wherein the type of theparticular wireless device is defined at least in part by the data rateof the particular device; and producing a control signal based on thetype of the particular wireless device for controlling the powertransmitted from the particular wireless device, and transmitting thecontrol signal.
 20. The method of claim 19 wherein the type of theparticular wireless device is defined at least in part by the quality ofservice requirement of the particular wireless device.
 21. The method ofclaim 19 wherein the control signal controls the power transmitted bythe particular wireless device such that wireless devices withproportionately higher data rates produce proportionately higher powerlevels as received by the base station.
 22. A method for controlling thepower transmitted by wireless devices of mixed typescomprising:receiving a composite spread signal of the signalstransmitted by a plurality of wireless devices; retrieving a unique codefrom memory corresponding to a particular wireless device which istransmitting and using the unique code to partially despread thecomposite spread signal; determining the current power received from andthe type of the particular wireless device, wherein the type of theparticular wireless device is defined at least in part by the quality ofservice requirement of the particular wireless device; and producing acontrol signal based on the type of the particular wireless device forcontrolling the power transmitted from the particular wireless device,and transmitting the control signal.
 23. The method of claim 22 whereinthe control signal controls the power transmitted by the particularwireless device such that wireless devices with proportionately higherquality of service requirements produce proportionately higher powerlevels as received by the base station.
 24. The method of claim 23 andfurther wherein the control signal controls the power transmitted by theparticular wireless device such that wireless devices withproportionately higher data rates produce proportionately higher powerlevels as received by the base station.